page_title: Greater Green River Basin
section_title: Source rocks, traps, and seals
hierarchical_section_title: Greater Green River Basin / Source rocks, traps, and seals
caption_attribution_description: English: A generalized cross section of the Upper Cretaceous Units shown from west to east along Southwestern Wyoming.
context_page_description: The Greater Green River Basin is a 21,000 square mile basin located in Southwestern Wyoming. The Basin was formed during the Cretaceous period sourced by underlying Permian and Cretaceous deposits. The GGRB is host to many anticlines created during the Laramide Orogeny trapping many of its hydrocarbon resources. It is bounded by the Rawlins Uplift, Uinta Mountains, Sevier overthrust belt, Sieria Madre Mountains, and the Wind River Mountain Range. The Greater Green River Basin is subdivided into four smaller basins the Green River Basin, Great Divide Basin, Washakie Basin, and Sand Wash Basin. Each of which possesses hydrocarbons that have been economically exploited. There are 303 named fields throughout the basin the majority of which produce natural gas, the largest of these gas fields is the Jonah Field.
context_section_description: There are many source rocks in the GGRB, up to 9 viable units, but the most abundant producers of hydrocarbons are the Permian Phosphoria Formation, the Cretaceous Mowry Shale, and the Cretaceous Mesaverde Group.  The Cretaceous source rocks are all marine shales that were deposited in a foreland basin created by the Cretaceous seaway. The marine shales experienced subsidence from the erosion of the Sevier Orogeny as well as Progradational accumulation that topped these anoxic marine shales with clastic alluvium. The clastic alluvium units now serve as a great reservoir rock for the marine shales deposited from the Permian into the Cretaceous.  
  Phosphoria Formation is made up of Permian Shales. It is believed that the organic rich shales are the primary source to much of the oil in the region. It is thought that the oil from these shales have migrated into the Pennsylvanian Tensleep Formation, and Paleozoic reservoirs of Central and Eastern Wyoming. Due to its carbonate and chert rich depositional environment, the oil found in the Phosphoria Formation as a high sulfer content making it Type-IIS kerogen. This is important to note because sulfur rich oils have been known to mature at much lower temperatures than normal. The Tensleep Formation is the most prominent reservoir rock hosting approximately 142 million barrels of oil with about 12 fields producing from this unit. The Phosphoria Formation was sealed by the marine shale units of the Triassic Dinwoody Formation. This shale seal was broken during the Laramide Orogeny leading to the migration of oil into the Tensleep Formation. The oil now is trapped in anticlines formed by the Laramide. 
  The Mowry Shale is a well-known source rock of Paleozoic reservoirs in Wyoming with the highest total organic content in the area. It is known to source the Dakota Sandstone and Frontier Formation both prolific reservoirs in the Rocky Mountain Region. The Mowry Shale is oil prone for the most part due to the collection of Type-II kerogen at deposition. The Mowry is unique because it is sealed by marine shales and trapped by both anticlines and faults. The Mowry Shales are estimated to hold 6.6 million barrels of oil and about 2 billion cubic feet of gas. 
  The Cretaceous Mesaverde Group supplies much of the gas to GGRB. The Mesaverde Group was a product of two major transgressions and regressions that lasted approximately 6 million years followed by another sequence that lasted 3 million years. Though much of the Mesaverde units were eroded and this is observed by the unconformity that splits the lower Mesaverde Group from the Upper. The Mesaverde Group is dominated by Type-III Kerogen making it a great source for gas and a decent source for oil. The Mesaverde Group is predominately sealed by marine shales that overlie the group. The Mesaverde Group experiences anticline traps, fault traps, and stratigraphic pinch-out traps in the fields it functions as source rock for through out the GGRB. The Mesaverde has an estimated production level of 2.3 million barrels of oil, and about 25.83 trillion cubic feet of gas making the Mesaverde Group the ideal source for gas exploration.
caption: A generalized cross section of the Upper Cretaceous Units shown from west to east along Southwestern Wyoming.
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